As Richard Stinear mentioned recently "Scrum is a hungry Beast, that wants to be feed constantly by Product owner". Lets see how Product Owner could escape this end-less-loop.
Gabrielle Benefield recently published by Twitter the Double O Model (see graph below). As I understood it will be part of her new Book, that comes out soon :-). It shows the 2 O's, where on the left hand side Product Owner is creating new Options and Innovations that will bring valuable Outcome. On the other side we see the delivery cycle, that runs experiments with common Output like Stories, Bugfixes, etc. Those impact are measured/adapted and flow back to Create Options O.
What is danger now if a Product Owner is fully occupied in the delivery O, without any time left for Innovation.
Some Product Owners are captured in delivering Output, instead of caring about valuable Outcome
Gabrielle Benefield, 10/2013
In other Words Team and Product Owner are just focused to deliver fast, but wrong, non-valuable Output. To get back to the left O it's recommended to constantly do a critical review of your current top Backlog Items and check there Outcome. As Alternativ go back to your stakeholders, the team and ask for the 2 most valuable Requests each and try to calculate the costs if Item wont be Done.